[core]* AVR: Set Optiboot as default bootloader for Nano. This is the bootloader installed on new Arduino Nano boards. If you have a Nano with the old bootloader you must select Tools > Processor > ATmega328P (Old Bootloader) to upload.* AVR core has been moved to its own repository: https://github.com/arduino/ArduinoCore-avr* Updated toolchain to gcc 5.4.0